Pigmented paper coating formulations generally comprise an aqueous synthetic polymer binder emulsion and pigment and may contain other additives typically used in the art. Illustrative of the polymer binders in the emulsions are vinyl acetate polymers, including vinyl acetate/ethylene and vinyl acetate/alkyl acrylate copolymers, and styrene/butadiene polymers, the polymers also generally containing a copolymerized ethylenically unsaturated mono- or dicarboxylic acid. Key properties required of a paper coating formulation include gloss, dry pick strength, ink holdout, rheology and wet pick strength. Vinyl acetate polymers are normally deficient with respect to providing, in combination, superior dry pick and wet pick strengths and good gloss. While it is desirable to have a vinyl acetate polymer binder which demonstrates both superior dry pick and wet pick strengths and gloss, previous attempts to improve dry pick strength and/or gloss resulted in an undesirable trade-off in other key properties such as emulsion stability, rheology, and, most importantly, the wet pick strength. Paper coatings containing vinyl acetate/ethylene copolymer binders usually lack sufficient wet pick resistance for use on high gloss paper grades that are intended for offset printing.
It is known in the art that softer copolymer binders respond better to the paper supercalendering operation, consequently providing the paper sheet with higher finished gloss. Although gloss specifications on coated paper products encompass a broad range, it is generally felt desirable to improve the gloss of coatings containing vinyl acetate polymers.
U.S. Pat. No. 4,395,499 discloses high strength pigments binders for paper coating having increased water retention and stability. The coating compositions contain an aqueous synthetic polymer latex comprising a dispersed interpolymer of a vinyl ester, a polyethylenically unsaturated comonomer selected from the group consisting of triallyl cyanurate, triallyl isocyanurate, diallyl maleate, diallyl fumarate, divinyl benzene, and diallyl phthalate, and an ethylenically unsaturated mono- or dicarboxylic acid or half ester thereof.
U.S. Pat. No. 4,144,212 discloses air-curing copolymer latexes suitable for use in paints and like coating applications. The air-curing copolymer latex comprises an aqueous dispersion of the copolymer of a mixture of copolymerizable monomers consisting essentially of (a) about 1-20% dicyclopentadienyl acrylate or dicyclopentadienyl methacrylate, (b) about 20-99% alkyl acrylate or methacrylate, (c) 0-5% acrylic acid or methacrylic acid, and (d) 0-85% other monoethylenically unsaturated copolymerizable monomers including, for example, vinyl esters such as vinyl acetate.
U.S. Pat. No. 4,309,330 discloses a copolymer emulsion comprising a copolymer obtained by copolymerizing (a) a dicyclopentadiene derivative, (b) an alpha,beta-unsaturated monomer having one or more OH groups, (c) an alpha,beta-unsaturated monomer copolymerizable with the components (a) and (b), followed by the reaction of the resulting copolymer with (d) a partial allyl ether of polyhydric alcohol having one or more terminal isocyanate groups. The copolymer emulsion can be crosslinked and cured at normal temperatures to give coating films showing hardness, water resistance, corrosion resistance and solvent resistance.
U.S. Pat. No. 4,100,133 discloses autoxidizable coating or impregnating composition comprising (a) a copolymer of 5 to 50 wt% dicyclopentadienyl acrylate with 50 to 95 wt% of at least one other monethylenically unsaturated comonomer, (b) a non-volatile reactive monomer, (c) a polyvalent metal-containing complex or salt that catalyzes the oxidative curing of (a) and (b), and a volatile oxime stabilizer.